Tuesday, March 18, 2014

Fraudster Michael Mann has published an article in Scientific American today entitled "Why Global Warming Will Cross a Dangerous Threshold in 2036," subtitled, "Emitting carbon dioxide at current rates will soon push Earth’s temperature up by 2 degrees Celsius. Here’s how to make the calculation yourself."

Mann appears to suggest that global temperatures will increase an additional 2C over the next 22 years from now to 2036, but doesn't mention he's talking about 2C warming total since pre-industrial times. Since the globe has warmed 0.7-0.8C since pre-industrial times, that would be an additional ~1.2C over the next 22 years.

Mann then proceeds in the article to go through his sciencey-sounding calculations to arrive at the dangerous threshold year of 2C warming by 2036, but his radiative calculations are just more hockey stick CAGW propaganda for the following reasons [and others]:

Global warming of 0.3C plus 0.8C since pre-industrial times would total to 1.1C, only about one-half of the 2C increase that Mann exaggerates below.

Even if radiative forcing did control the surface temperature [it doesn't- convection, phase change, pressure, atmospheric mass do], Mann's radiative forcing calculations are exaggerated by at least 3.8 times due to false assumptions of water vapor positive feedback. Mann's claims are once again shown to be just more hockey stick propaganda, oblivious to the abject failure of climate models based upon these same calculations.

If the world continues to burn fossil fuels at the current rate, global warming will rise 2 degrees Celsius by 2036, crossing a threshold that many scientists think will hurt all aspects of human civilization: food, water, health, energy, economy and national security. In my article "False Hope" in the April 2014 Scientific American, I reveal dramatic curves that show why the world will reach this temperature limit so quickly, and also why the recent slowdown in the rate of temperature increase, if it continues, will only buy us another 10 years.

These numbers come from calculations made by me and several colleagues. We plugged values of Earth’s “equilibrium climate sensitivity”—a common measure of the heating effect of greenhouse gases—into a so-called energy balance model. Scientists use the model to investigate possible climate scenarios.

You can try this exercise yourself. The text below explains the variables and steps involved. You can download the climate data here and the model code here. And you can compare your results with mine, which are here. You can also change the variables to see what other future scenarios are possible. One note: the model runs on MatLab software, which can be obtained here.

We employed a simple zero-dimensional Energy Balance Model (“EBM”—see references 1 through 5 below) of the form

C dT/dt = S(1-a)/4 + FGHG -A-B T + w(t)

to model the forced response of the climate to estimate natural and anthropogenic radiative forcing.

T is the temperature of Earth’s surface (approximated as the surface of a 70-meter-depth, mixed-layer ocean covering 70 percent of Earth’s surface area). C = 2.08 x 108J K-1m-2 and is an effective heat capacity that accounts for the thermal inertia of the mixed-layer ocean, but does not allow for heat exchange with the deep ocean as in more elaborate “upwelling-diffusion models” (ref. 6). S ≈ 1370 Wm-2 is the solar constant, and a ≈ 0.3 is the effective surface albedo. FGHG is the radiative forcing by greenhouse gases, and w(t) represents random weather effects, which was set to zero to analyze the pure radiative forced response.

The linear “gray body” approximation (ref. 3) LW = A+B T was used to model outgoing longwave radiation in a way that accounts for the greenhouse effect. The choice A = 221.3 WK-1m-2 and B = 1.25 Wm-2 yields a realistic preindustrial global mean temperature T = 14.8 oC and an equilibrium climate sensitivity (ECS) of DT2xCO2 = 3.0oC, consistent with midrange estimates by the International Panel on Climate Change (ref. 7). B can be varied to change the ECS of the EBM. For example, the higher value B = 1.5 Wm-2 yields a more conservative ECS of DT2xCO2 = 2.5oC.

Energy Balance Model Simulations

Historical Simulations. The model was driven with estimated annual natural and anthropogenic forcing over the years A.D. 850 to 2012. Greenhouse radiative forcing was calculated using the approximation (ref. 8) FGHG = 5.35log(CO2e/280), where 280 parts per million (ppm) is the preindustrial CO2 level and CO2e is the “equivalent” anthropogenic CO2. We used the CO2 data from ref. 9, scaled to give CO2e values 20 percent larger than CO2 alone (for example, in 2009 CO2 was 380 ppm whereas CO2ewas estimated at 455 ppm). Northern Hemisphere anthropogenic tropospheric aerosol forcing was not available for ref. 9 so was taken instead from ref. 2, with an increase in amplitude by 5 percent to accommodate a slightly larger indirect effect than in ref. 2, and a linear extrapolation of the original series (which ends in 1999) to extend though 2012.

Estimated past changes in solar irradiance were prescribed as a change in the solar constant S whereas forcing by volcanic aerosols was prescribed as a change in the surface albedo a. Solar and volcanic forcing were taken from the General Circulation Model (GCM) simulation of ref. 3 described in the section above, with the following modifications: (1) solar forcing was rescaled under the assumption of a 0.1 percent change from Maunder Minimum to present, more consistent with recent estimates (ref. 9); (2) volcanic forcing was applied as the mean of the latitudinally varying volcanic forcing of ref. 9; (3) values for both series were updated through 2012.

Future Projections: For the purpose of the “business as usual” future projections, we have linearly extrapolated the CO2 radiative forcing forward to 2100, based on the trend over the past decade (which is roughly equivalent, from a radiative forcing standpoint, to a forward projection of the exponential historical trajectory of CO2 emissions). We assume constant solar output, and assume no climatically significant future volcanic eruptions.

We have assumed that tropospheric aerosols decrease exponentially from their current values with a time constant of 60 years. This gives a net anthropogenic forcing change from 2000 to 2100 of 3.5 Wm-2, roughly equivalent to the International Panel on Climate Change’s 5th assessment report “RCP6” scenario, a future emissions scenario that assumes only modest efforts at mitigation.

Stabilization Scenarios: For the stabilization scenarios, we relax (with a 20-year time constant) the CO2 concentration to a maximum specified value at 2100. We considered cases both where the anthropogenic tropospheric aerosol burden is assumed to (a) decrease exponentially from their current values with a time constant of 60 years, as in the future projections discussed in the previous section, and alternatively (b) remain constant at its current value.

Additional Details. Sensitivity analyses of the historical simulations were performed by Mann et al 2012 (ref. 4) with respect to (i) the equilibrium climate sensitivity assumed (varied from DT2xCO2 = 2-4 oC); the (ii) solar scaling (0.25 percent in place of 0.1 percent Maunder Minimum to present change); (iii) the volcanic aerosol loading estimates used; and (iv) the scaling of volcanic radiative forcing with respect to aerosol loading to account for possible size distribution effects. All of the alternative choices described above were found to yield qualitatively similar results.

Michael Mann, a man who never saw a fray he didn't want to enter, has decided to enter the climate sensitivity fray, with an article published simultaneously in the Huffington Post and Scientific American. Some of it is a bit odd to tell the truth.

For example, take this bit about the IPCC's decision to reduce the lower bound on its estimate of climate sensitivity down to 1.5°C.

The IPCC had lowered the bottom end of the range, down from the two degrees C it had set in its Fourth Assessment Report, issued in 2007. The IPCC based the lowered bound on one narrow line of evidence: the slowing of surface warming during the past decade—yes, the faux pause.

However, those who have read the relevant parts of the Fifth Assessment and indeed those who are familiar with the recent Lewis/Crok report on climate sensitivity will be aware that the IPCC actually gave a completely different explanation for their decision to reduce the lower bound.

The lower temperature limit of the assessed likely range is thus less than the 2°C in the AR4, but the upper limit is the same. This assessment reflects improved understanding, the extended temperature record in the atmosphere and ocean, and new estimates of radiative forcing.

I don't know about you, but I count that as three lines of evidence not one.